This invention relates generally to refractively scanned interferometer/spectrometers and more particularly to a novel, improved, miniature, opto-mechanical head incorporated in a Fourier Transform Spectrometer (FTS) that utilizes only two, substantially identical, optical components that enable the maintenance of a very high throughput efficiency.
Optical spectroscopy is at present the most used analytical technique for both laboratory and remote sensing. To advance the capability of FTS apparatus, two beam interferometers of the Michelson type and of related, refractively scanned instruments have been developed. An example of the latter type of apparatus is my U.S. Pat. No. 4,654,530 for a REFRACTIVELY SCANNED INTERFEROMETER granted on 31 Mar., 1987, which presents a long term, alignment stable and vibration resistant, portable, optical structure that represented an improvement in the FTS art and has been particularly useful for remote sensing applications under field conditions. However, a need exists for an apparatus with even greater sensitivity, stability, smaller size and weight coupled with improved radiometric performance.
As pointed out in my afore-mentioned patent, reflective scanning had deficiencies that were overcome by refractive scanning. Also, a linearly scanned, wedge-shaped transmission window to create a differential in optical path length, where the varying thickness of the wedge shape resulted in a proportional optical retardation, had deficiencies. Known devices of this type caused complications in design and had sensitivity to external forces from hostile environments. The wedge was also an additional component to the standard Michelson configuration and thus added to the cost and subtracted from the efficiency.
Although the Michelson type of instruments has been refined to reflect a high degree of efficiency, they usually suffer in performance in hostile and adverse environments unless heavy and costly vibration cancelling mounts are provided. Furthermore, their sensitivity to mechanical disturbances has all but limited their use to infrared and millimeter wavelengths. Few attempts have been made to extend their use to the short wavelength visible and ultraviolet spectrum.
It has become axiomatic that the larger the instrument and the more parts there are to the optical system, the greater the difficulty in maintaining alignment and, consequently, accuracy. The environmental stability of interferometric devices deteriorates roughly with volume.
Although the prior art has made strides toward the production of a small, hand portable, inexpensive device which is accurate, even though it is subjected to a hostile environment, as evidenced by my afore-mentioned U.S. patent, a rugged, miniaturized device, which solves the problems of the prior art and at the same time provides an interferometer that achieves improved resolution, has proved elusive. Laboratory devices of large size have heretofore been required for accurate measurement.